When you run 2.0 as a single node, it doesn’t create system databases on startup. You have to do this manually:
curl -X PUT http://127.0.0.1:5984/_users
curl -X PUT http://127.0.0.1:5984/_replicator
curl -X PUT http://127.0.0.1:5984/_global_changes
See the next section for the cluster setup instructions.